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CRAPTERFIVE <br />The highest CALPUFF-calculated 24-hour extinction from Yankee Gulch <br />the Piceance and Pazachute facilities) was 0.194 Mm-' at the Flat Tops Cla <br />24-hour extinction from PM.,. emissions was 0.017 Mm"'. Therefore. addi <br />I azea is 0.211 Mm"'. Given the <br />Draft EIS Recisions <br />:>x emissions (both <br />]: area. The highest <br />the two imoacts <br />extinction of 16.69 <br />Mm"', the extinction chance is 1.26% or 0.1 deciview. Since this value is not ¢reater than the 1.0 <br />deciview just noticeable change threshold, the Yankee Gulch facilities would not significantly <br />effect the visibility at the Class I azea. <br />hour extinction from cumulative source NO, emissions <br />cumulative oil and <br />was calculated at the Flat <br />both Yankee Gulch and <br />Class I azea as 1.536 <br />Since PM10 emission data were not significant from the oil and gas cumulative sources, the <br />highest 24-hour extinction from Yankee Gulch PM,~ emissions (0.017 Mm-')was added to <br />dative extinction at the Flat Tops Class I azea is 1.553 <br />16.69 Mm"' the extinction chani?e is 9.3% or 0.9 <br />deciview. Since this value is not greater than 1.0 deciview just noticeable change threshold, the <br />predicted cumulative visibility impacts aze not expected to be perceptible. <br />Granulative visibility impacts at sensitive Class II azeas (Dinosaur and Colorado National <br />Monuments) from Yankee Gulch Project NO, and PM10 emissions and other oil and gas NO, <br />emissions were also calculated. The deciview change for Colorado National Monument is 0.13 <br />deciviews, and for Dinosaur National Montunent is 0.16 deciviews. <br />A 1.0 deciview change is considered "potentially significant," as adopted by the Grand Canyon <br />Visibility Transport Commission and reported in Pitchford and Malm (1994). A deciview is <br />defined as about a 10 percent change in extinction coefficient, which is a small but perceptible <br />scenic change under many circumstances. The 1.0 deciview value corresponds to a 2 to 5 ... <br />Page 4-32 <br />TABLE 4.5-10 (modified) <br />ACCELERATED DEVELOPMENT ALTERNATIVE -CLASS II INCREMENT <br />ANALYSIS FOR PICEANCE SITE <br /> <br />PoButantlParameter PM10 <br />24-honr PM1° <br />Annutil NO, <br />Annual <br />Maximum Piceance-only <br />Increment Concentration (µg/m') 61.8 21.3 42.6 <br />Percent of Class I[ increment (%) 206 125 170 <br />Maximum Cumulative Inaemeot <br />Concentration (µg/m') 87.330.3 23.721.1 55.246.3 <br />Percent of Class II Increment (%) 291234 139330 221385 <br />i <br />Source: RTP 1998a • <br />